Steady growth of the demand for fossil fuels has resulted in major economic and environmental challenges in the past few years. Energy, as a measure of wealth, has turned into an international commodity and as such, new technologies for optimal harvest, storage, transmission, and consumption of various energy forms have occupied the center stage of the research and academic communities. Wind energy as a sustainable resource (i.e. abundant, affordable, environmentally neutral, and sizable) has attracted considerable attention among the alternative sources of energy. Doubly Fed Induction Generators (DFIG) have demonstrated superior advantages in comparison to other forms of electric machinery in the optimal harvest of wind energy as an adjustable speed generator system. Although control of DFIG has been addressed in the literature in length, its interaction with the power grid still looks far from exhausted. In particular, the effects of system unbalance and system harmonics have been shown to be of great concern. This is primarily due to the fact that system unbalance and harmonics can generate unwanted torque undulations that can potentially undermine the mechanical integrity of the tower and reduce the lifetime of the moving components that are attached to the generator shaft.
The enabling technology for optimal calculation of the rotor currents is based on the field reconstruction method (FRM). FRM is an analytical tool for approximation of the magnetic field distribution within the airgap of an unsaturated electromechanical energy converter using a truncated generalized Fourier series. The basis function used in this Fourier expansion is computed using simple (one time) magneto-static field solution of the stator/rotor excitation by a dc-current. Once the FRM formulation is set up, it is capable to predict the magnetic field distribution and hence, the tangential/normal components of the magnetic forces for any arbitrary distribution of the stator and rotor currents. This in turn paves the road for optimization of the field distribution by computing the desired excitation of the stator and rotor currents in a very short time (about two orders of magnitude faster than Finite Element Analysis).
The embodiment described herein solves these problems and others by proposing a new method of using the Field Reconstruction Method and numerical optimization method in judiciously selecting rotor currents to actively eliminate/mitigate torque pulsations. The method may be augmented to a tool for elimination of the vibrations caused from mechanical origins.